Abstract
PurposeDue to multiple beamlets in the delivery of highly modulated volumetric arc therapy (VMAT) plans, dose delivery uncertainties associated with small‐field dosimetry and interplay effects can be concerns in the treatment of mobile lung lesions using a single‐dose of stereotactic body radiotherapy (SBRT). Herein, we describe and compare a simple, yet clinically useful, hybrid 3D‐dynamic conformal arc (h‐DCA) planning technique using flattening filter‐free (FFF) beams to minimize these effects.Materials and MethodsFifteen consecutive solitary early‐stage I‐II non‐small‐cell lung cancer (NSCLC) patients who underwent a single‐dose of 30 Gy using 3–6 non‐coplanar VMAT arcs with 6X‐FFF beams in our clinic. These patients’ plans were re‐planned using a non‐coplanar hybrid technique with 2–3 differentially‐weighted partial dynamic conformal arcs (DCA) plus 4–6 static beams. About 60–70% of the total beam weight was given to the DCA and the rest was distributed among the static beams to maximize the tumor coverage and spare the organs‐at‐risk (OAR). The clinical VMAT and h‐DCA plans were compared via RTOG‐0915 protocol for conformity and dose to OAR. Additionally, delivery efficiency, accuracy, and overall h‐DCA planning time were recorded.ResultsAll plans met RTOG‐0915 requirements. Comparison with clinical VMAT plans h‐DAC gave better target coverage with a higher dose to the tumor and exhibited statistically insignificance differences in gradient index, D2cm, gradient distance and OAR doses with the exception of maximal dose to skin (P = 0.015). For h‐DCA plans, higher values of tumor heterogeneity and tumor maximum, minimum and mean doses were observed and were 10%, 2.8, 1.0, and 2.0 Gy, on average, respectively, compared to the clinical VMAT plans. Average beam on time was reduced by a factor of 1.51. Overall treatment planning time for h‐DCA was about an hour.ConclusionDue to no beam modulation through the target, h‐DCA plans avoid small‐field dosimetry and MLC interplay effects and resulting in enhanced target coverage by improving tumor dose (characteristic of FFF‐beam). The h‐DCA simplifies treatment planning and beam on time significantly compared to clinical VMAT plans. Additionally, h‐DCA allows for the real time target verification and eliminates patient‐specific VMAT quality assurance; potentially offering cost‐effective, same or next day SBRT treatments. Moreover, this technique can be easily adopted to other disease sites and small clinics with less extensive physics or machine support.
Highlights
With the development of more precise and accurate treatment delivery, stereotactic body radiation therapy (SBRT) treatment of medically inoperable early‐stage non‐small‐cell lung cancer (NSCLC) patients shows higher tumor local‐control rate and minimal treatment‐related toxicity.[1‐5] For the selected peripherally located NSCLC patients; single‐dose of SBRT has become a curative treatment option as shown by the randomized trials.[6‐13] For instance, Videtic and colleagues[7] compared 2 single‐fraction SBRT dosing schemes of 30 and 34 Gy for 80 medically inoperable early stage‐I NSCLC patients
The CI with hybrid 3D‐dynamic conformal arc (h‐dynamic conformal arcs (DCA)) plans were slightly higher than clinical volumetric modulated arc therapy (VMAT) plan, providing a little leeway could be beneficial for target coverage while respecting the organs‐at‐ risk (OAR) dose. h‐DCA plans
A simple, yet clinically useful h‐DCA planning technique was devised for lung SBRT treatments
Summary
With the development of more precise and accurate treatment delivery, stereotactic body radiation therapy (SBRT) treatment of medically inoperable early‐stage non‐small‐cell lung cancer (NSCLC) patients shows higher tumor local‐control rate and minimal treatment‐related toxicity.[1‐5] For the selected peripherally located NSCLC patients; single‐dose of SBRT has become a curative treatment option as shown by the randomized trials.[6‐13] For instance, Videtic and colleagues[7] compared 2 single‐fraction SBRT dosing schemes of 30 and 34 Gy for 80 medically inoperable early stage‐I NSCLC patients. With the development of more precise and accurate treatment delivery, stereotactic body radiation therapy (SBRT) treatment of medically inoperable early‐stage non‐small‐cell lung cancer (NSCLC) patients shows higher tumor local‐control rate and minimal treatment‐related toxicity.[1‐5]. Videtic and colleagues[7] compared 2 single‐fraction SBRT dosing schemes of 30 and 34 Gy for 80 medically inoperable early stage‐I NSCLC patients. Both treatment schedules provided similar tumor local‐control and overall survival rates with minimal pulmonary toxicity. There has been growing interest in the clinical use of flattening filter free (FFF) beams to deliver lung SBRT treatment.[14‐18]. FFF‐beams have much higher dose rates compared to traditional flattened‐beams that use flattening filters (FF). FFF beams can reduce beam on time ( beneficial for single large dose treatment), resulting in better patient comfort and reducing dose delivery uncertainty due to less intrafraction motion error and can potentially reduce out‐of‐field dose with less head scatter and electron contamination.[16]
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